[en] A seventeen year-old boy developed left sided chorea in a few days, subsequently involving the four limbs. Although he presented a marfanoid phenotype, genetic analysis of the Fibrillin 1 was normal. The genes for familial chorea and Huntington's disease were also negative. Biological tests showed normal serum homocystein, but revealed very high levels of anti-beta2-GP1 IgG, anticardiolipin and lupus anticoagulant, which remained at similar values for a period of over three months. Electroencephalogram and cerebral magnetic resonance imaging (MRI) showed no abnormalities. Brain PET-scan disclosed bilateral striatal hypermetabolism. The patient was treated with methylprednisolone and low dose of acetylsalicylic acid. He improved markedly after six weeks of treatment, and choreic movements disappeared completely after two months. A control PET-scan performed at this time showed reversion of striated hypermetabolism to a normal pattern. The pathogenic aspects of this relatively rare case of chorea are discussed.